Interactions between Herbicidal Carbamates and Growth Regulators

Interactions between carbamate and growth regulator herbicides were antagonistic both in whole plants and in plant segments. When combinations of isopropylm-chlorocarbanilate (chlorpropham) and (2,4-dichlorophenoxy)acetic acid (2,4-D) were applied to the foliage of either redroot pigweed (Amaranthus retroflexusL.) or pale smartweed (Polygonum lapathifoliumL.), the severe twisting effects of 2,4-D were greatly reduced. This interaction did not involve differential movement or metabolism of either herbicide. The induced elongation of soybean hypocotyl sections by the three growth regulators 2,4-D, 3,6-dichloro-o-anisic acid (dicamba), and 4-amino-3,5,6-trichloropicolinic acid (picloram) was inhibited in the presence of either chlorpropham orS-ethyl dipropylthiocarbamate (EPTC). Similarly, curvature tests using soybean (Glycine max(L.) Merr.) hypocotyl sections showed the curvature induced by the growth regulators to be almost completely eliminated by the presence of the carbamates.